1. Field of the Invention
The present invention relates to an electronic device, which is operated with a power source having a low output voltage and generates power using environmental energy.
2. Description of the Related Art
FIG. 8 shows a block diagram of a conventional electronic device. The electronic device includes a power source 101 for supplying power, a load circuit 107, a switch 103 for connecting the power source 101 and the load circuit 107, a switch control circuit 102 for controlling the switch 103, a capacitor 105 for storing power used for driving the switch control circuit 102, a charge/discharge control circuit 104 for supplying power from the power source 101 to the capacitor 105 when the power stored in the capacitor 105 becomes scarce, and an operation monitoring circuit 106 for monitoring an operation state of the load circuit (for example, see JP 2001-69687 A).
The load circuit 107 consumes power even in a standby state where the circuit is not being operated, so energy use efficiency has been very poor. In order to solve this problem, an attempt is made to minimize wasteful power by interrupting the connection between the power source 101 and the load circuit 107 by the switch 103, in the standby state.
In a case where the supply of power from the power source 101 is interrupted, the switch control circuit 102 controls the switch 103 using the power stored in the capacitor 105. When the power stored in the capacitor 105 becomes scarce, the switch control circuit 102 turns on the switch 103, and allows the charge/discharge control circuit 104 to supply the power to the capacitor 105. When the power stored in the capacitor 105 becomes sufficient, the switch control circuit 102 turns off the switch 103 again, and returns to the standby state. The charge/discharge control circuit 104 has functions of supplying the power supplied from the power source 101 to the capacitor 105, and preventing a flow of a current from the capacitor 105 to the load circuit 107.
When the load circuit attempts to enter the operation state, the operation monitoring circuit 106 sends a signal to the switch control circuit 102 to turn on the switch 103, and supplies the power of the power source 101 to the load circuit 107. The operation monitoring circuit 106 is connected to the capacitor 105, and is operated using the power of the capacitor 105. Therefore, even when the switch 103 is turned off and the power of the power source 101 is not supplied to the operation monitoring circuit 106, the operation monitoring circuit 106 can be operated.
With the circuits thus configured, standby power of the electronic device can be reduced.
In such the conventional electronic device, in order to control the switch 103, it is necessary that the switch control circuit 102 and the operation monitoring circuit 106 are constantly operated. The two circuits are operated using the power stored in the capacitor 105, and when the power stored in the capacitor 105 becomes scarce, the two circuits should be supplied with the power from the power source 101. In a case where the switch control circuit 102, the charge/discharge control circuit 104, the capacitor 105, the operation monitoring circuit 106, and the switch 103 provided for reducing the wasteful power when the load circuit 107 is in a standby state use the power to control the switch 103 for interrupting the wasteful power, reduction in power consumption will not be achieved.
Further, although the operation monitoring circuit 106 constantly monitors the operation of the load circuit 107, in order to operate the load circuit 107, it is necessary to supply the power to the load circuit 107. Since the power source 101 and the load circuit 107 are interrupted by the switch 103, the power stored in the capacitor 105 needs to be used for operating the load circuit 107. If the power consumption immediately after the starting of the load circuit 107 is extremely large, the load circuit 107 cannot be operated with the power of the capacitor 105, and the operation monitoring circuit 106 cannot detect the operation of the load circuit 107. Therefore, in the conventional electronic device, the load circuit 107 needs to be set so as to be operated with the power stored in the capacitor 105 at the time of starting.